This invention relates to a network attached storage (NAS) having a clustered configuration.
There has been proposed a network attached storage (NAS) that is a storage system connected to a network and used as a shared disk for computers connected to the network. The NAS is composed of a server including a network interface and disk drives storing data. Further, there is disclosed a NAS that includes a plurality of servers and has a clustered configuration in which each of the servers is connected to a network (see, for example, U.S. Pat. No. 6,671,773).
In U.S. Pat. No. 6,671,773, network elements, a switching fabric, and disk elements correspond to the servers of the NAS. The plurality of network elements provided can share a file system. In addition, the plurality of disk elements provided allow migration of the file system on a disk basis.
On the other hand, a network file system (NFS) has been proposed as one of file systems that allow an access to files distributed on a network. According to NFSv4 (RFC 3530), which is the most updated version of the NFS protocol specification as of now, when a file system is migrated between servers, the migration source server responds to an access requested from a client to the file system to notify the client of information on a location of the file system at a migration destination (see the IETF home page at the Internet URL: http://www.ieff.org/home.html, (a search was made online for this specification on Nov. 11, 2004)). Therefore, the client can access the file system at the migration destination based on the notified location information. In addition, a file handle, which is an identifier used for an access, consists of two types, a volatile file handle and a persistent file handle. When the file system is migrated, the volatile file handle thereof can be set to invalid.